A machine or factory that processes cereal grains such as wheat and rye into flour. An enterprise of the flour-milling industry at which grain is converted into flour.
Flour-milling technology has developed greatly, from the primitive devices of prehistoric man to modern mechanized flour mills. The most ancient tools for grinding grain were the mortar and stamp; they were followed by the buhrstone. They were all manually operated. The use of waterwheels began in ancient states. Windmills, which still used the buhrstone as the milling instrument, were first built in the Middle Ages. With the appearance of windmills of advanced construction, grain processing also improved. The invention of the steam engine furthered the development of flour mills. The first steam-driven flour mills appeared in the early 19th century.
In modern flour mills, the grain is unloaded from trucks, railroad cars, and ships by mechanical and pneumatic apparatus. The grain is stored in an elevator according to type and qualitative indicators (moisture content and vitreousness). Grain affected by pests or blight is stored separately.
Grain is prepared for milling in the cleaning section of a flour mill. Such preparation includes removal of impurities by means of separators, screening machines, and magnetic devices; dry scouring (in scouring mills) or wet scouring (in washing machines); grain conditioning, which is treatment with water and heat; and blending of various types of grain before milling.
In the grinding section, the grain undergoes three major operations in gradual reduction: preliminary crushing, or breaking; enrichment of the resultant middlings; and fine grinding of the enriched middlings into flour. The grain is milled in roll mills operating together with sifters that sort the milled grain product according to size and, to a certain extent, quality. After enrichment and milling on a battery of roll mills, the middlings are converted into a finer product, called coarse meal, which is then milled into flour. Such a milling procedure permits separation from the grain of the maximum amount of shell-free endosperm in the form of flour.
In the sifting section, the flour is poured by machine into sacks and weighed automatically. As many as 30 types of machines may be involved in the production process; grain at a plant with average output may travel up to 5 km from the point of unloading at the elevator to discharge as flour from the sifting section.
Flour mills are characterized by high power availability (8–10 kilowatts per production worker). The production process is mechanized and continuous. The total annual power consumption of flour mills reaches tens of millions of kilowatt-hours. For example, a flour mill that processes 800 tons of wheat daily into high-grade flour, with an elevator with a capacity of 100,000 tons of grain and suction apparatus for unloading grain from barges, has an annual power requirement of about 25 million kW-hr under normal operation. Modern mills are completely equipped with suction transportation for conveying the grain and intermediate products.